1. Field of the Invention
The present invention relates to a radio communication system, and more particularly, to a radio communication system and method for transmitting and receiving a multimedia broadcast/multicast service.
2. Description of the Related Art
Radio communication systems have remarkably improved; however, when providing communication services dealing with a large capacity of data, radio systems have not provided the same functions provided by wired communication systems. Accordingly, countries around the world are developing technologies, such as IMT-2000, a wireless communication system enabling a large capacity of data communication. Cooperation between many countries is currently progressing to create a specification for the technology.
A universal mobile telecommunications system (UMTS) is a third generation mobile communication system evolving from the Global System for Mobile Communications (GSM) system, which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based a GSM core network and Wideband Code Division Multiple Access (W-CDMA) technologies.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States of America, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for the purpose of creating a specification for standardizing the UMTS. The work towards standardizing the UMTS performed by the 3GPP has resulted in the formation of five technical specification groups (TSGs), each of which is directed to forming network elements having independent operations.
Each TSG develops, approves, and manages a specification in a related region. Among them, a radio access network (RAN) group (TSG-RAN) develops a specification for the function, items desired, and interface of a UMTS terrestrial radio access network (UTRAN), which is a new RAN for supporting a W-CDMA access technology in the UMTS.
Referring to FIG. 1, a related art UMTS network 1 structure is shown. The UMTS broadly comprises a user equipment (UE or terminal) 10, a UMTS Terrestrial Radio Access Network (UTRAN) 100, and a core network (CN) 200. The UE 10 is connected to the core network 200 through the UTRAN 100. The UTRAN 100 configures, maintains, and manages a radio access bearer for communications between the UE 10 and the core network 200 to meet end-to-end quality-of-service requirements.
The UTRAN comprises a plurality of radio network subsystems (RNS) 110, 120, each of which comprises one radio network controller (RNC) 111 for a plurality of base stations, or Node Bs 112, 113. The RNC 111 connected to a given Node B 112, 113 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 10 operating in one cell. The controlling RNC 111 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 112, 113 may receive an uplink signal from a UE 10 and may transmit a downlink signals to the UE. Each Node B 112, 113 serves as an access point enabling a UE 10 to connect to the UTRAN 100, while an RNC 111 serves as access point for connecting the corresponding Node Bs to the core network 200.
The interface between the UE 10 and the UTRAN 100 is realized through a radio interface protocol established in accordance with 3GPP radio access network specifications. Referring to FIG. 2, a related art radio interface protocol structure used in the UMTS is shown. The radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and is divided vertically into a user plane for data transmissions and a control plane for transfer of control signaling. The user plane is the region in which user traffic information, such as voice signals and IP (Internet Protocol) packets is transferred. The control plane is the region for carrying control information for the maintenance and management of the interface. In FIG. 2, protocol layers may be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of an open system interconnection (OSI) model that is a well-known in the art.
The first layer (L1) is a physical layer (PHY) providing information transfer service to a higher layer using various radio transmission techniques. The physical layer is linked to a medium access control (MAC) layer located above it. Data travels between the MAC layer and the PHY layer via a transport channel.
The second layer (L2) comprises the MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer and a packet data convergence protocol (PDCP) layer. The MAC layer of the second layer (L2) provides assignment service of a MAC parameter for assigning and re-assigning a radio resource. It is connected to an upper layer, i.e., the radio link control (RLC) layer by a logical channel. Various logical channels may be provided according to the type information transmitted. Generally, when control plane information is transmitted, a control channel is used. When user plane information is transmitted, a traffic channel is used.
The RLC layer of the second layer (L2) supports the transmission of reliable data and is responsible for the segmentation and concatenation of RLC service data units (SDUs) delivered from a higher layer. The size of the RLC SDU is adjusted for the processing capacity in the RLC layer and a header is appended to form an RLC protocol data unit (PDU) for delivery to the MAC layer.
The formed units of service data and protocol data delivered from the higher layer are stored in an RLC buffer of the RLC layer. The RLC services are used by service-specific protocol layers on the user plane, namely a broadcast/multicast control (BMC) protocol and a packet data convergence protocol (PDCP), and are used by a radio resource control (RRC) layer for signaling transport on the control plane.
The broadcast multicast control (BMC) layer schedules a cell broadcast (CB) message delivered from the core network 200 and enables the cell broadcast message to be broadcast to the corresponding UEs 10 in the appropriate cell. Header information, such as a message identification, a serial number, and a coding scheme, is added to the cell broadcast message to generate a broadcast/multicast control message for delivery to the RLC layer.
The RLC layer appends RLC header information and transmits the thus-formed message to the MAC layer via a common traffic channel (CTCH) as a logical channel. The MAC layer maps the CTCH to a forward access channel (FACH) as a transport channel. The transport channel is mapped to a secondary common control physical channel (SCCPCH) as a physical channel.
The packet data convergence protocol (PDCP) layer serves to transfer data efficiently over a radio interface having a relatively small bandwidth. The PDCP layer uses a network protocol such as IPv4 or IPv6 and a header compression technique for eliminating unnecessary control information utilized in a wire network. The PDCP layer enhances transmission efficiency since only the information essential to the header is included in the transfer.
The radio resource control (RRC) layer handles the control plane signaling of the network layer (L3) between the UEs 10 and the UTRAN 100 and controls the transport and physical channels for the establishment, reconfiguration, and release of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for data transfer between the UE 10 and the UTRAN 100.
Establishment of an RB determines the regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 10 and an RRC layer of the UTRAN 100, the UE 10 is said to be in the RRC-connected state. Without such connection, the UE 10 is in an idle state.
For reference, the RLC layer can be included in the user plane or the control plane according to a layer connected above it. For example, when the RLC layer is part of the control plane, data is received from the RRC layer. In other cases, the RLC layer is part of the user plane.
A particular radio bearer used for exchanging an RRC message or an NAS message between a terminal and the UTRAN 100 is referred to as a signaling radio bearer (SRB). When the SRB is set up between a particular terminal and the UTRAN 100, there can exist an RRC connection between the terminal and the UTRAN 100. The terminal which forms the RRC connection is said to be in the RRC connected mode (or state), and the terminal which does not form the RRC connection is said to be in the idle mode (or state). If the terminal is in the RRC connected mode, the RNC checks and manages a location of the corresponding terminal according to a cell unit. When the terminal gets into the RRC connected mode, the RNC sends a signaling message to the UTRAN 100. The terminal in the RRC connected mode may be further divided into a CELL_DCH mode, a CELL_PCH mode, a URA_PCH mode and a CELL_FACH mode.
For those UEs in the idle state, URA_PCH mode, or CELL_PCH mode, a discontinuous reception (DRX) method is employed to minimize power consumption. In the DRX method, a Secondary Common Control Physical Channel (SCCPCH), onto which a Paging Indicator Channel (PICH) and a Paging Channel (PCH) is mapped, is discontinuously received by the UE 10. During the time periods when the PICH or the SCCPCH is not received, the UE is in a sleep mode state. The UE wakes up at every DRX cycle length (discontinuous receiving period length) to receive a paging indicator (PI) of the PICH.
The terminal in the RRC connected mode may additionally form a signaling connection with the core network 200. This signaling connection refers to a path for exchanging a control message between the terminal and the core network 200. The RRC connected mode refers to a connection between the terminal and the UTRAN 100. Accordingly, the terminal informs the core network 200 of its location or requests a particular service using the signaling connection. To obtain the signaling connection, the terminal should be in the RRC connected mode.
Hereafter, Multimedia Broadcast/Multicast Service (MBMS or MBMS service) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs 10 using a downlink-dedicated MBMS radio bearer. The MBMS radio bearer may utilize both point-to-multipoint and point-to-point radio bearer services.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is transmitting multimedia data to all UEs within a broadcast area, for example the domain where the broadcast area is available. The multicast mode is for transmitting multimedia data to a specific UE group within a multicast area, for example the domain where the multicast service is available.
FIG. 3 is a diagram showing procedures of the MBMS service in the multicast mode. Here, the UMTS network is shown providing a specific MBMS service (a first service) using the multicast mode. A terminal (UE1) is also shown receiving the specific service (the first service).
When the UMTS network 1 provides a specific MBMS using the multicast mode, UEs 10 to be provided with the service must first complete a subscription procedure establishing a relationship between a service provider and each UE individually. Thereafter, the subscriber UE 10 receives a service announcement from the core network 200 confirming subscription and including, for example, a list of services to be provided.
The subscriber UE 10 must “join,” or participate in, a multicast group of UEs receiving the specific MBMS, thereby notifying the core network 200 of its intention to receive the service. Terminating participation in the service is called “leaving.” The subscription, joining, and leaving operations may be performed by each UE 10 at any time prior to, during, or after the data transfer.
While a specific MBMS is in progress, on or more service sessions may sequentially take place, and the core network 200 informs the RNC 111 of a session start when data is generated by an MBMS data source and informs the RNC of a session stop when the data transfer is aborted. Therefore, a data transfer for the specific MBMS may be performed for the time between the session start and the session stop, during which time only participating UEs 10 can receive the data.
To achieve successful data transfer, the UTRAN 100 receives a notification of the session start from the core network 200 and transmits an MBMS notification to the participating UEs 10 in a prescribed cell to indicate that the data transfer is imminent. The UTRAN 100 uses the MBMS notification to count the number of participating UEs 10 within the prescribed cell. Specifically, the UTRAN 100 can perform a function which counts the number of terminals which expect to receive the specific MBMS service within a specific cell.
Through the counting process, it is determined whether the radio bearer providing the specific MBMS service is one for a point-to-multipoint transmission or a point-to-point transmission, or if the radio bearer is not to be set. To select the MBMS radio bearer (RB) for a specific service, the UTRAN 100 sets a threshold value corresponding to the UE 10 count, whereby a low UE count establishes a point-to-point MBMS radio bearer and a high UE count establishes a point-to-multipoint MBMS radio bearer.
The radio bearer established is based on whether the participating UEs 10 need to be in the RRC-connected state. When a point-to-point RB is established, all of the participating UEs 10 which expect to receive the service are in the RRC connected state. When a point-to-multipoint RB is established, it is unnecessary for all of the participating UEs 10 which expect to receive the service to be in the RRC connected mode since the point-to-multipoint RB enables reception by UEs in the idle state. Furthermore, based on the counted result, if no terminal wishes to receive the specific MBMS service, the UTRAN 100 does not establish any radio bearer and the MBMS service data is not transmitted. Thus, radio resources may be wasted by establishing the radio bearer even though no terminal desires the service. Also, the UTRAN 100 transmits the MBMS service data received from the core network 200 during one session of the MBMS service using the established radio bearer.
In the counting process, the UTRAN 100 has no information on terminals in the RRC idle state. Therefore, if the UTRAN 100 requests a counting of terminals in the RRC idle state, subscribed to a specific MBMS service, the terminals should form the RRC connection with the UTRAN 100 and inform the UTRAN 100 that they would receive the specific MBMS service.
However, if a terminal has formed a signaling connection with a Serving GPRS Support Node (SGSN), the SGSN informs the UTRAN 100 of MBMS related information of the terminal. The information includes a list of MBMS services the terminal has subscribed to. Therefore, because the UTRAN 100 can recognize whether terminals have subscribed to a specific MBMS service, the terminals do not respond to the counting request of the UTRAN 100. Furthermore, terminals which have not formed a signaling connection with the SGSN, but are in the RRC connected state, can inform the UTRAN 100 of the MBMS services they have subscribed to when forming the RRC connection with the UTRAN 100. Accordingly, the UTRAN 100 can count the number of terminals desiring to receive the specific MBMS service without any response sent by the terminals in the RRC connected state.
The UTRAN 100 can perform the counting process not only at the beginning of the MBMS service but also in the middle of one session of the MBMS service. This is necessary since the number of terminals expecting to receive the MBMS service in a cell is variable because of events such as a terminal moving to another cell during the MBMS session in process, turning off power, or stopping the subscription of the MBMS service. Accordingly, in order to establish the radio bearer efficiently, the UTRAN 100 can perform the counting process during the MBMS session in process.
However, in this counting process, the following problems may occur when counting the number of terminals desiring to receive the MBMS service and establishing the radio bearer. A terminal is able to get information related to several MBMS services through the MBMS service announcement so that it may subscribe to a plurality of MBMS services. If the terminal stays in the RRC connected state, the UTRAN 100 can recognize all the MBMS services the terminal has subscribed to. Thus, when the UTRAN 100 performs the counting process for a certain MBMS service, a terminal in the RRC connected state and subscribed to the corresponding MBMS service, is added in the number of terminals desiring the MBMS service to be provided.
When the terminal simultaneously receives services it has subscribed to, an event may occur when several services among the subscribed services may not be received due to the terminal's limited capability. For example, a terminal having subscribed to two MBMS services has one SCCPCH through which the MBMS services can be received. If each MBMS service is transmitted through different SCCPCHs, respectively, using the point-to-multipoint RB in a cell, the terminal can receive only one of the subscribed MBMS services due to its limited capability. However, the UTRAN 100 is unable to recognize that the terminal can not receive one of the MBMS services. As a result, the UTRAN 100 performs the counting process and wrongfully considers the terminal as receiving all two MBMS services it has subscribed to. The UTRAN 100 then establishes a radio bearer based on this information.
The error occurring during the counting process causes radio resources to be wasted. As a further example, it is assumed that six terminals are in a cell, and all six terminals have subscribed to an MBMS service A and an MBMS service B. Moreover, all six terminals are in the RRC connected state and can receive services through one SCCPCH. It is also assumed that a threshold value for establishing a point-to-multipoint RB is set at 3. The MBMS service A is being transmitted through the point-to-multipoint RB in a cell and the UTRAN 100 has received a session start notification for the MBMS service B from the core network 200. In this case, the UTRAN 100 may determine there are six terminals which expect to receive the MBMS service B and thus establish the point-to-multipoint RB.
However, if an SCCPCH different from an SCCPCH used for transmitting the MBMS service A is used for transmitting the MBMS service B, then the six terminals may receive only one of the MBMS services A and B due to the their limited capabilities. Thus, either the MBMS service A or the MBMS service B is received according to a user's selection. A situation may occur where five terminals determine to receive the MBMS service A and one terminal determines to receive the MBMS service B. Accordingly, since there is only one terminal desiring to receive the MBMS service B, the UTRAN 100 should establish the point-to-point RB because the number terminals desiring the MBMS service B is below the threshold value of 3. However, the related art UTRAN 100 establishes the point-to-multipoint RB with respect to the MBMS service B because it wrongfully counts all six terminals for receiving the service B. The error occurs because the UTRAN 100 has no information regarding the capabilities of the terminals, service selection of the user, or the like. Unfortunately, the resources required for establishing the point-to-multipoint RB corresponds to several times that of the point-to-point RB. As a result, due to the error occurring during the counting process in the related art, radio resources are wasted and the number of services to be simultaneously provided in one cell is limited.